The present invention relates to the use of foamable compositions for packaging purposes. In a number of packaging applications, fragile articles or those otherwise needing protection from undesired movement or breakage, particularly items with irregular shapes and sizes, have been packed in protective foamed polymer packaging materials, such as injection molded styrofoam, styrofoam chips, or other similar materials.
One technique for packaging articles in foam comprises generating the foam in place while the articles are being packaged. For example, when certain chemicals are mixed, they form polymeric products while at the same time generating gases, such as carbon dioxide and water vapor. If such chemicals are selected as being those that harden relatively quickly, they can be used to form hardened polymer foams in which the foam is produced by the gaseous carbon dioxide and water vapor leaving the mixture as it hardens.
One technique for foam-in-place packaging is to place the object to be packaged in a container, cover it with a polymer film or other material which will protect it from liquids, inject a certain amount of foamable composition into the remainder of the container, and then close the container. As the composition foams, it fills the remainder of the container, forming a custom-shaped foam cushion surrounding the article.
For larger volume packaging operations, i.e., those requiring a number of foam protective packages to be made in relatively rapid succession, a number of automated devices have been developed and are assigned to the assignee of the present invention. Exemplary devices are described and claimed in U.S. Pat. Nos. 4,674,268; 4,800,708; and 4,854,109.
In other circumstances, however, the need for foam-in-place packaging still exists, but the use of automated machinery is unnecessary or undesired from a cost, efficiency, or other standpoint. In such circumstances, foam-in-place packaging can be accomplished with a supply of foamable chemicals, usually two, and an injection gun connected to the supplies of the respective chemicals. The chemicals are mixed within the gun to form the foamable composition. Examples of earlier versions of such guns include those described in U.S. Pat. Nos. 3,687,370; 3,945,569; 4,023,733; 4,159,079; and 4,426,023.
As known to those familiar with these devices and with foam-in-place resin systems, the resins tend to react quickly enough to often harden within, and then clog, the injection device. Thus, an improvement in such devices was the replacement of an integral mixing chamber in guns, such as those described in the aforementioned patents, with a detachable mixing chamber or cartridge, such as that shown in U.S. Pat. Nos. 4,469,251; 4,568,003; and 4,898,327. The contents of the U.S. Pat. No. 4,898,327 are incorporated entirely herein by reference and are assigned to the assignee of the present invention. Additionally, several applications for related improvements in the cartridge injection system are set forth in the following copending applications, each of which is likewise incorporated entirely herein by reference: Bertram et al, Ser. No. 07/730,708; filed Jul. 16, 1991 for "Improved Cartridge Port Design for Dispensing Foam Precursors; and Sperry et al, Ser. No. 07/767,033; filed Sep. 26, 1991 for "Improved Pumping and Cleaning System for Foam In Place Injection Cartridges. By providing a small, detachable injection cartridge, the problems of cleaning or replacing a clogged device are minimized.
As seen from each of these patents and applications, the cartridge is a generally cylindrical device, which in actual practice can vary in size, but in typical embodiments is approximately 23/4 inches in length and approximately 5/8 inch in diameter. In operation, the cartridge usually serves as the mixing chamber for two foam precursors, such as the typical combination of a liquid organic resin and a polyisocyanate, which react to form polyurethane, carbon dioxide, and water vapor. As set forth above, because water vapor and carbon dioxide are formed as gases, they tend to bubble out of the resulting polyurethane as it hardens, leaving behind a foamed structure.
As seen in the patents which relate to cartridge-type devices, the chemicals to be ejected are mixed and valved by adding the chemicals separately to the cartridge and then moving a valving rod laterally within the cartridge housing to open and close the cartridge. The forces applied to the cartridge during the valving operations are rather significant: up to 900 pounds when polyurethane has hardened on the end of the cartridge and adhered the valving rod to the face of the cartridge. This force is applied to the cartridge both laterally; i.e, in the direction of the valving rod's movement; and perpendicularly. To date, the detachable cartridges have been held in place in the gun systems describe in these patents by a single-threaded stud that depends from the barrel of the cartridge. This stud, although generally of relatively small size; i.e., approximately 1/8 inch in diameter and approximately 5/8 inch in length; was expected to successfully bear all of the lateral and perpendicular forces applied during foam injection.
It has been discovered, however, that the forces applied to such cartridges are significant enough to reduce their lifetime below that which should otherwise be expected, or to cause breakdown and leakage of the entire apparatus.
Therefore, there exists a need for a better structure and technique for fastening the detachable injection cartridge in place more securely with respect to the chemical supply and to the valving mechanism that operates it while still maintaining the advantages of the detachable injection cartridge.